錯誤創建在谷歌數據存儲實體與JDO

Question

我創建與JDO在谷歌App Engine的Web應用程序，我得到一個JDOFatalUserException：

javax.jdo.JDOFatalUserException: Detected attempt to establish User(15) as the 
parent of SessionToken("VALID_USER_TOKEN") but the entity identified 
by SessionToken("VALID_USER_TOKEN") has already been persisted 
without a parent. A parent cannot be established or changed once an 
object has been persisted. 

我有類用戶，其中有一個SessionToken。我想將用戶和SessionToken都存儲在數據存儲中。用戶密鑰是自動生成的，而SessionToken密鑰是由我生成的。

@PersistenceCapable 
public class User { 

    @PrimaryKey 
    @Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY) 
    private Key key; 
    @Persistent 
    private SessionToken sessionToken; 

    //getters and setters... 
} 

和：

@PersistenceCapable 
public class SessionToken { 

    @PrimaryKey 
    private Key token; 

    public SessionToken(Key token) { 
    this.token = token; 
    } 

    //getters and setters... 
} 

然後我想創建一個用戶，所以我做的：

PersistenceManager pm = PMF.get().getPersistenceManager(); 

User user = new User(); 

Key key = KeyFactory.createKey(SessionToken.class.getSimpleName(), 
    "VALID_USER_TOKEN"); 
user.setSessionToken(new SessionToken(key)); 

try { 
    pm.makePersistent(user); 
} finally { 
    pm.close(); 
} 

以下是完整的異常轉儲：

javax.jdo.JDOFatalUserException: Detected attempt to establish User(15) as the parent of SessionToken("VALID_USER_TOKEN") but the entity identified by SessionToken("VALID_USER_TOKEN") has already been persisted without a parent. A parent cannot be established or changed once an object has been persisted. 
    at org.datanucleus.api.jdo.NucleusJDOHelper.getJDOExceptionForNucleusException(NucleusJDOHelper.java:498) 
    at org.datanucleus.api.jdo.JDOPersistenceManager.jdoMakePersistent(JDOPersistenceManager.java:736) 
    at org.datanucleus.api.jdo.JDOPersistenceManager.makePersistent(JDOPersistenceManager.java:756) 
    at com.mockgaeapp.UsersEndpoint.register(UsersEndpoint.java:38) 
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) 
    at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source) 
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source) 
    at java.lang.reflect.Method.invoke(Unknown Source) 
    at com.google.appengine.tools.development.agent.runtime.Runtime.invoke(Runtime.java:115) 
    at com.google.api.server.spi.SystemService.invokeServiceMethod(SystemService.java:239) 
    at com.google.api.server.spi.SystemServiceServlet.execute(SystemServiceServlet.java:161) 
    at com.google.api.server.spi.SystemServiceServlet.doPost(SystemServiceServlet.java:120) 
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:637) 
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:717) 
    at org.mortbay.jetty.servlet.ServletHolder.handle(ServletHolder.java:511) 
    at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1166) 
    at com.google.appengine.api.socket.dev.DevSocketFilter.doFilter(DevSocketFilter.java:74) 
    at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157) 
    at com.google.appengine.tools.development.ResponseRewriterFilter.doFilter(ResponseRewriterFilter.java:123) 
    at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157) 
    at com.google.appengine.tools.development.HeaderVerificationFilter.doFilter(HeaderVerificationFilter.java:34) 
    at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157) 
    at com.google.appengine.api.blobstore.dev.ServeBlobFilter.doFilter(ServeBlobFilter.java:61) 
    at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157) 
    at com.google.apphosting.utils.servlet.TransactionCleanupFilter.doFilter(TransactionCleanupFilter.java:43) 
    at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157) 
    at com.google.appengine.tools.development.StaticFileFilter.doFilter(StaticFileFilter.java:125) 
    at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157) 
    at com.google.appengine.tools.development.BackendServersFilter.doFilter(BackendServersFilter.java:97) 
    at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157) 
    at org.mortbay.jetty.servlet.ServletHandler.handle(ServletHandler.java:388) 
    at org.mortbay.jetty.security.SecurityHandler.handle(SecurityHandler.java:216) 
    at org.mortbay.jetty.servlet.SessionHandler.handle(SessionHandler.java:182) 
    at org.mortbay.jetty.handler.ContextHandler.handle(ContextHandler.java:765) 
    at org.mortbay.jetty.webapp.WebAppContext.handle(WebAppContext.java:418) 
    at com.google.appengine.tools.development.DevAppEngineWebAppContext.handle(DevAppEngineWebAppContext.java:94) 
    at org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:152) 
    at com.google.appengine.tools.development.JettyContainerService$ApiProxyHandler.handle(JettyContainerService.java:409) 
    at org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:152) 
    at org.mortbay.jetty.Server.handle(Server.java:326) 
    at org.mortbay.jetty.HttpConnection.handleRequest(HttpConnection.java:542) 
    at org.mortbay.jetty.HttpConnection$RequestHandler.content(HttpConnection.java:938) 
    at org.mortbay.jetty.HttpParser.parseNext(HttpParser.java:755) 
    at org.mortbay.jetty.HttpParser.parseAvailable(HttpParser.java:218) 
    at org.mortbay.jetty.HttpConnection.handle(HttpConnection.java:404) 
    at org.mortbay.io.nio.SelectChannelEndPoint.run(SelectChannelEndPoint.java:409) 
    at org.mortbay.thread.QueuedThreadPool$PoolThread.run(QueuedThreadPool.java:582) 

我不明白錯誤，因爲我不堅持SessionToken持續用戶之前的對象...

這個異常是什麼意思？

Answer 1

你的代碼告訴JDO有User和SessionToken對象，其中子實體應該有它的父父的鍵（在數據存儲中的術語）之間的「擁有」關係，當你明確地設置鍵無父。

請嘗試使用'unowned' relationship。